Hello everyone and welcome to this week's video! Today I'm going to be
talking about catalytic converters,
more specifically three-way catalytic converters. And what three-way means is
it's trying to eliminate Nitrogen Oxide emissions, Carbon Monoxide emissions, and
Hydrocarbon emissions; or, in other words, unburned fuels.
So, the way it does this inside of a catalytic converter,
you've got these two blocks and one is a reduction catalyst, and the other is an
oxidation catalyst, and the the reduction catalyst is made up of platinum and
rhodium, and the oxidation catalyst is made up of platinum and palladium.
So what happens is, you've got... from combustion you've got CO2, y'got carbon
monoxide,
you've got nitrogen oxides, got oxygen water, and unburned fuel, all coming into
this catalytic converter.
now the first step it goes through, is this reduction catalyst, platinum rhodium
and what happens is, you're trying to eliminate the nitrogen oxides.
So the nitrogen oxide will come into this catalyst and, so inside of this it's
just a bunch of tiny little ducts, little micro ducts and there's thousands of
them, and that's what the air is passing through so you're trying to maximize
surface area with that design.
So the nitrogen dioxide will come in and the nitrogen bond with the oxygen isn't
as strong as its bond with the catalyst, so once the bond with catalyst so it will
bond the catalyst and when it does that it'll weaken its bond with the two
oxygens. So the two oxygens will separate off, and they may go off, or they can join
together. But eventually these two oxygens are going to find another oxygen
to pair up with so that they're O2 rather than just O, which is a little more stable.
So, once these nitrogens are all alone here on this catalyst they'll move along
the surface, they want to meet up with another nitrogen, that- they prefer that
bond rather than the catalyst. So once they bond with
another nitrogen, their bond with the catalysts weaken and they split off and-
and go off to the next step.
And so then you're just left with nitrogen and oxygen, which are both
perfectly harmless gases in your catalyst, the surface is ready to
continue this function with other elements and other molecules. So then
after you go through the first step
we've eliminated NO2 and and and NO, and- so now we just have N2, O2, CO, CO2
H2O and our hydrocarbons.
So the next step is this oxidation catalyst, which is made of platinum and
palladium.
So what happens in here, is the catalyst surface wants to bond with oxygens.
So what will happen is the carbon monoxide and the oxygen molecules will
come and they'll bond with the surface.
Now once the oxygen molecules bond with the surface, they'll split up and when
they split up, the bond with the carbon monoxide is stronger than just by
themselves. So they'll bond to the carbon monoxide, they'll form carbon dioxide, and
then the bottom of the catalyst is weakened
so this will go off and out the out the catalytic converter continue on through
the exhaust and then your catalyst surface once again is free and ready
to continue doing this-
this function here to eliminate carbon monoxide.
So then- also within this you're trying to get rid of these hydrocarbons and so
we have these freed up oxygens we've got hydrocarbons-
if you haven't watched my video on air-fuel ratio stoichiometric air-fuel ratio,
that may help. Basically your hydrocarbons and oxygen are going to
form H2O and CO2. They're going to combust within this- react within
this catalytic converter, and so they'll be forming the harmless H2O, and then the
kind of harmful CO2. So catalytic converters do not eliminate CO2 but they
do eliminate the other gases, NO2, NO, and CO.
So after it's gone through this phase, then you're just left with N2, O2, CO2
and H2O, and catalytic converters can do this on about a 90 of percent efficient
basis so they're still going to be some of these harmful gases leftover, but
about ninety percent of them
it can convert and some obviously are better than others.
In catalytic converters, one thing to note is they work best once heated up,
that's how the reactions occur a little more easily.
So that's catalytic converters and their function. If you haven't already, i would
recommend watching my video on exhaust systems, it kind of gives you the basic
overview
Thanks for watching!